1. Field of Invention
The present invention relates, in general, to a hybrid transmission, and more particularly, to a structure of a transmission adapted to transfer power from each of an engine and a motor to driving wheels.
2. Description of Related Art
In general, hybrid vehicles are vehicles using two or more energy sources and are mostly used in a combination of an existing engine using fossil fuels and at least one motor using electrical energy, although various other methods may be used depending on the combination of many energy sources.
Depending on whether the engine and/or the motor is operated, the hybrid vehicles can realize an electric vehicle (EV) mode driven by only the motor, a hybrid electric vehicle (HEV) mode driven by both the engine and the motor, and an engine-only mode driven by only the engine. Also, the hybrid vehicle can operate a generator using kinetic energy in the vehicle instead of wasting energies in conventional friction braking during an idle stop and during deceleration of the vehicle. Therefore, compared to conventional vehicles, hybrid vehicles can enhance the fuel efficiency by reducing the fuel consumption through regenerative braking, in which the generated electric energy is stored in a battery and then reused for driving the vehicle or the like.
A variety of hybrid transmissions are used in such hybrid vehicles, among them is a transmission using only a single motor as shown in FIG. 1.
Specifically, an automatic transmission 500, in which a conventional torque converter is eliminated, is connected to an engine 504 via a friction clutch 502, and a motor 506 is connected to an input shaft of the automatic transmission 500. Alternatively, the automatic transmission 500 may be replaced with a conventional continuously variable transmission (CVT) and the like.
In the hybrid transmission as described above, the EV mode driving can be carried out using the motor 506 during a vehicle launch, and then at a vehicle speed higher than a predetermined value, the engine 504 is started and the friction clutch 502 is engaged such that the acceleration ability and the fuel efficiency can be enhanced through a torque distribution between the engine 504 and the motor 506. Also, during braking, the braking energy can be recovered as electric energy through the motor 506, leading to enhancement of the fuel efficiency. In addition, since only one motor is used in contrast to other conventional hybrid transmission structures using two motors, an obvious advantage can be achieved in terms of cost-savings.
However, hybrid transmissions having such a structure experience some problems. For example, an impact can be caused when the clutch is engaged after starting of the engine. Also, when a charged amount of the battery is insufficient or a capacity of the motor is small, namely when low-speed hill climbing using the engine torque is required continuously, performance of the hybrid transmissions can be degraded. Performance degradation includes an impact due to a slip of the clutch, instability of speed control, or a thermal deterioration of the clutch. In addition, since an input shaft for the engine power and an input shaft for the motor power are identical, utilization of an optimal efficiency operating point of the motor, in which the motor has a number of revolutions per minute higher than those of the engine, can be restricted and thus enhancement of the fuel efficiency cannot be sufficiently realized.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.